Mobile telephone operators around the world have built an international “network of networks”. A subscriber to a particular mobile network can receive calls when roaming in a visited mobile network. This is shown in FIG. 1, to which reference is now made, which is schematic illustration of a prior art communication system which enables roaming. The communication system comprises a home mobile network (HMN) 10 and a visited mobile network (VMN) 12 connected by a telephone infrastructure 14. A mobile telephone 16 belonging to a user that has subscribed to the HMN 10 is roaming in the VMN 12. The HMN 10 comprises a mobile switch center (MSC) 18, a home location register (HLR) 20 and a short message service center (SMSC) 22. Similarly, the VMN 12 comprises an MSC 18′, a visited location register (VLR) 24 and an SMSC 22′. The HMN 10 is connected to a voice mail system (VMS) 26.
When the mobile telephone 16 is turned on in the VMN 12, the mobile telephone 16 registers itself in the VLR 24, which notifies the HLR 20 via the telephone infrastructure 14 that the mobile telephone 16 is accessible via the MSC 18′. When the HMN 10 receives a call for the mobile telephone 16, its MSC 18 interrogates the HLR 20 and transfers the call over the telephone infrastructure 14 to the MSC 18 of the VMN 12, which transfers the call to the mobile telephone 16.
If the mobile telephone 16 is turned off or busy, the incoming call to the MSC 18 is forwarded to the VMS 26, where a message may be recorded. In the event of a message recorded in the voice mailbox of the VMS 26 for the mobile telephone 16, the VMS 26 sends a standard notification to the SMSC 22. There are a number of problems with notifying the roaming mobile telephone 16 that a message has been recorded in the VMS 26 and with enabling the mobile telephone 16 to retrieve the message.
One problem is that the notification is not always transferred successfully to the VMN 12. For example, if the HMN 10 and VMN 12 are not both Global System for Mobile communication (GSM) networks, then it may not be technically possible to transfer the notification. As a further example, the telephone infrastructure 14 may block notifications for technical or commercial reasons.
Another problem is that even if the mobile telephone 16 receives the notification, the short code that the user of the mobile telephone 16 dials in order to access the voice mailbox while in the HMN 10 is generally irrelevant in the VMN 12. For example, if the user accesses the voice mailbox directly by dialing ‘634’ while in the HMN 10, dialing “634” while in the VMN 12 does not enable the user to access the voice mailbox. Therefore, the user must call the HMN 10 using a full international number (14 digits when calling direct, 35 digits when using “call back” services). The user then has to dial the voice mailbox number and password (an additional 4 to 10 digits). It is unlikely that the user will complete this complex long dialing procedure correctly. It is also unlikely that the user will try again after failing the first time. Another contributing factor to the failure of the long dialing procedure is that dial tone multi-frequency (DTMF) signals are transmitted with low quality over international telephone lines. In principle, it is possible to eliminate the dialing of the voice mailbox number and password by using the calling line identification (CLI) of the mobile telephone 16 to identify which voice mailbox to use, but the CLI is also not always transmitted successfully over international telephone lines.
Even when the roaming user succeeds in accessing the voice mailbox and retrieving the message, the user pays expensive international telephone rates. For this reason, most roaming users do not retrieve their voice mail messages, and many corporations even instruct their employees not to retrieve voice mail messages while roaming. This leads to a loss of service to the users and to a loss of income to the mobile network operators.
U.S. Pat. No. 5,751,792 to Chau et al. describes a system and method for providing a message system subscriber with a roaming mailbox. The messages in the home mailbox are transferred to a temporary roaming mailbox at a roaming node. According to Chau, the visited mobile network (VMN) must either have a dedicated voice mail system (VMS) for roaming users or must allocate temporary mailboxes in the existing VMS of the VMN. There may not be room available in the existing VMS for allocation of temporary mailboxes. It is not clear when to delete an allocated temporary mailbox. Furthermore, mailboxes cost the VMN money and it may be complicated for the VMN to be reimbursed for this cost. The user will have to contend with an unfamiliar way to access and work with voice mail messages.
The European Telecommunications Standards Institute (ETSI) has set a new GMS standard called Customized Application of Mobile Enhanced Logic (CAMEL). The standard specifies all the components needed to let GSM network operators offer the Intelligent Network (IN) services they supply in their home country to customers that roam on foreign networks. A major disadvantage to CAMEL is that it requires an upgrade to the installed mobile network. This is an expensive and time-consuming procedure. Moreover, CAMEL-compatible components are not yet commercially available. Furthermore, non-GSM networks are not able to use CAMEL to offer IN services to roaming subscribers.